1. Field of the Invention
This invention relates to a novel phosphor, and more particularly to a cerium activated or cerium and terbium activated borate phosphor which emits blue to green light of high luminance.
2. Description of the Prior Art
As a cerium activated or cerium and terbium activated oxide phosphor, have been known in the art a cerium activated magnesium aluminate phosphor (CeMgAl .sub.11 O.sub.19, see Japanese Patent Public Disclosure No. 22,836/1977), a cerium and terbium activated magnesium aluminate phosphor [(Ce,Tb)MgAl.sub.11 O.sub.19, see the above Japanese Patent Public Disclosure No. 22,836/1977], a cerium activated yttrium silicate phosphor (Y.sub.2 SiO.sub.5 : Ce, see Japanese Patent Public Disclosure No. 37,914/1973), a cerium and terbim activated yttrium silicate phosphor (Y.sub.2 SiO.sub.5 :Ce,Tb, see Japanese Patent Laid Open No. 127,384/1978), a cerium activated calcium phosphate phosphor [Ca.sub.3 Ce(PO.sub.4).sub.3, see Japanese Patent Laid Open No. 57,480/1979], a cerium and terbium activated calcium phosphate phosphor [Ca.sub.3 (Ce,Tb)(PO.sub.4).sub.3, see the above Japanese Patent Laid Open No. 57,480/1979], a cerium and terbium activated boron oxide phosphor [(Ce,Tb).sub.2 O.sub.3. 3B.sub.2 O.sub.3, see Japanese Patent Laid Open No. 33,986/1978], etc. Generally, these cerium and terbium activated oxide phosphors emit blue to green light. That is, among these phosphors, the phosphor activated with cerium solely exhibits blue light emission caused by cerium. On the other hand, in the phosphor activated with both cerium and terbium, as the amount of terbium relative to the amount of cerium increases, the energy transmitted from cerium to terbium increases and therefore, the green light emission caused by terbium is gradually enhanced. When the amount of terbium relative to the amount of cerium is larger than a certain value, the phosphor exhibits grcen light emission.
The above-mentioned conventional cerium activated or cerium and terbium activated oxide phosphors emit blue to green light of considerably high luminance under excitation of ultraviolet rays, cathode rays, X-rays, vacuum ultraviolet rays, or the like. Therefore, these phosphors are useful for various applications, for example, such as fluorescent lamp, cathode ray tube, X-ray image converter and plasma display device, and some of them have been practically used. Needless to say, it is desirable that the luminance of these phosphors is to be as high as possible from the viewpoint of practical use thereof. Accordingly, it is desired to obtain a cerium activated or cerium and terbium activated oxide phosphor which emits light of higher luminance than the above-mentioned conventional cerium activated or cerium and terbium activated oxide phosphors.